xfstests: only run generic/300 on filesystems supporting fallocate()

Generic/300 fails when run on a test filesystem that does not support fallocate(), as in the case of an ext4 filesystem created without the extent feature or with the bigalloc feature. It uses fio's falloc ioengine to generate part of its I/O load, and both fallocates blocks and punches holes.

Verify that the test filesystem supports fallocate() before proceeding with the test, checking for both block allocation and hole punching capabilities. We need to use both _require_xfs_io_falloc and _require_xfs_io_falloc_punch because the latter does not currently test for block allocation support. Also, delete any pre-existing test output to avoid confusion with old results.

---
 tests/generic/300 | 11 +++++++++++
 1 file changed, 11 insertions(+)

index 7c60728..1bb2837 100755
@@ -44,6 +44,17 @@ _supported_os Linux
 _need_to_be_root
 _require_scratch
 
+# For this test, the test system's glibc and kernel and the test file system
+# must support both fallocating and hole punching.  We don't need xfs_io to
+# perform the test, but we can use it to verify these preconditions.  For now,
+# this allows us to avoid duplicating the following functions for fio or other
+# applications that might be used to generate I/O at the cost of picking up a
+# minor dependency on xfsprogs.
+_require_xfs_io_falloc
+_require_xfs_io_falloc_punch
+
+rm -f $seqres.full
+
 NUM_JOBS=$((4*LOAD_FACTOR))
 BLK_DEV_SIZE=`blockdev --getsz $SCRATCH_DEV`
 if [ $((BLK_DEV_SIZE)) -gt 1048576 ]

1.8.1.2